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Comparisons of the NGA Ground-Motion Relations
Abstract
The data sets, model parameterizations, and results from the five NGA models for shallow crustal earthquakes in active tectonic regions are compared. A key difference in the data sets is the inclusion or exclusion of aftershocks. A comparison of the median spectral values for strike-slip earthquakes shows that they are within a factor of 1.5 for magnitudes between 6.0 and 7.0 for distances less than 100 km.The differences increase to a factor of 2 for M5 and M8 earthquakes, for buried ruptures, and for distances greater than 100 km. For soil sites, the differences in the modeling of soil/sediment depth effects increase the range in the median long-period spectral values for M7 strike-slip earthquakes to a factor of 3. The five models have similar standard deviations for M6.5-M7.5 earthquakes for rock sites and for soil sites at distances greater than 50 km. Differences in the standard deviations of up to 0.2 natural log units for moderate magnitudes at all distances and for large magnitudes at short distances result from the treatment of the magnitude dependence and the effects of nonlinear site response on the standard deviation. DOI: 10.1193/1.2924363
... The use of various ground motion attenuation equations in seismic hazard assessment with different weights to overcome the disadvantages of each ground motion model is only carried out when no equation is appropriate for the study area. Moreover, Abrahamson et al., (2008) [22] made the comparisons of the NGA ground motion relations and noted that the NGA equations are all fairly similar, and all are reasonably constrained by the data. Therefore, the use of only one ground motion attenuation equation, which is appropriate for seismotectonic conditions of the study area, is adequate for seismic hazard assessment in order to avoid errors from inappropriate models. ...
... The use of various ground motion attenuation equations in seismic hazard assessment with different weights to overcome the disadvantages of each ground motion model is only carried out when no equation is appropriate for the study area. Moreover, Abrahamson et al., (2008) [22] made the comparisons of the NGA ground motion relations and noted that the NGA equations are all fairly similar, and all are reasonably constrained by the data. Therefore, the use of only one ground motion attenuation equation, which is appropriate for seismotectonic conditions of the study area, is adequate for seismic hazard assessment in order to avoid errors from inappropriate models. ...
... The value of V S30 is used in building codes [23,26,27]. It is also an important parameter to estimate site conditions used in ground motion prediction equations and seismic hazard assessments [22,28,29]. In the applications of engineering seismology, site effect is estimated by using empirical correlations of V S30 . ...
In this study, we have carried out the probabilistic seismic hazard analysis in Hanoi based on the latest seismotectonic data. The seismic hazard map shows peak ground acceleration values on rock corresponding to the 10% probability of exceedance in a 50-year time period (approximately return periods of 500 years). The calculated results reveal that the maximum ground acceleration can occur on rock in Hanoi is about 0.13 g corresponding to the shaking intensity level of VIII on the MSK-64 scale. The ground motion values calculated on rock vary according to the local site conditions. We have evaluated and corrected the local site effects on ground motion in Ha Dong district, Hanoi by using microtremor and borehole data. The Nakamura’s H/V spectral ratio method has been applied to establish a map of ground dominant periods in Ha Dong with a TS range of 0.6 - 1.2 seconds. The relatively high values of periods indicate that Ha Dong has soft soil and thick Quaternary sediments. The sediment thickness in Ha Dong is calculated to vary between 30 - 75 m based on ground dominant periods and shear wave velocity VS30 = 171 - 254 m/s. The results of local site effect on ground motion show that the 500-year return period peak ground acceleration in Ha Dong ranges from 0.13 g to 0.17 g. It is once again asserted that the seismic hazard in Hanoi is a matter of great concern, due not only to the relatively high ground acceleration, but also to the seismic characteristics of soil (low shear wave velocity, ground dominant period of approximately 1 second).
... The bridge is permanently monitored by the EPPO/ITSAK Institution in Thesaloniki and has been the basis of several system identification studies [29,30] The performance of the TIDs is analysed with respect to different cable geometries, subjected to earthquakes with various frequency contents, characterised by the seismic events' moment magnitudes M and sourceto-site distances R. In addition to the analysis of the TID performance with respect to M R ( , ), the current study also proposes a framework to select one single TID design to fulfil the performance criteria for multiple cables, as is desirable for practical application to a cablestayed bridge. The paper is structured in three main sections: the first section describes the structural models of the bridge, the cables and the TIDs, as well as the model for the synthetic seismic-ground motions as a function of M R ( , ); the second section consists of the core risk-assessment and performance-based design of the TIDs for the stay cables; and the third part consists of a numerical evaluation of the TID-controlled cables of the Evripos bridge subjected to the ground motions in the NGA West database [31]. ...
... Based on the analysis done in Section 3.2, the TID designed for Cable 11 was chosen as the unique TID to be installed for all cables on the bridge, based on the established criteria. To test the performance of the selected TID 11 for each cable to real ground-motion records, the mid-span uncontrolled and TID-controlled responses for each cable are calculated for approximately 3, 500 records in the NGA-West dataset [31]. Fig. 16 shows the NGA-West empirical tail probability- distribution functions of the mid-span responses for each of the 34 uncontrolled and controlled cables with the selected TID 11 . ...
This paper has a twofold aim: to assess the performance of tuned-inerter dampers (TIDs) to reduce vibrations in cable structures subjected to seismic ground motions; and to extend an existing TID-design method for cables to a practical scenario of multiple cables in a cable-stayed bridge. In this study, TIDs are installed between the cables and the bridge’s deck, the cables being excited at both their ends by the response of the bridge’s deck and pylon to seismic ground motions. The seismic hazard is described in a general manner by rates of earthquakes and synthetic ground-motion time histories with respect to their moment magnitudes and epicentral distances. Two approaches that use an existing deterministic method to design TIDs to reduce vibrations in cables are discussed. The first one, perhaps more effective but impractical, assumes that each cable’s response is reduced by its own independently-designed TID. The second approach, more realistic and practical, proposes the design of one single TID for all cables to reduce their mid-span response in an optimal way. Numerical results are shown for cable models in the Evripos Bridge in Greece, for which a unique TID is designed for all cables in the bridge, subjected to a hypothetical seismic-hazard scenario. It is shown that the TID-controlled cables have generally a better response, that is a lower average maximum absolute mid-span displacement for most of the cables, and lower variability in the response.
... The relative scarcity of larger magnitude earthquake recordings hampers the reliability of seismic hazard assessment in SISZ, because there is no data to properly constrain the possible non self-similar ground motion scaling at larger magnitudes and/or the increasing saturation of near-fault peak amplitudes with increasing magnitudes, as generally observed in earthquake ground motions of shallow crustal earthquakes in interplate tectonic regions [1,[25][26][27]. Moreover, previously published seismic hazard studies for Iceland have relied on either a single theoretical GMM using (at the time, even more limited) local data from the SISZ [28,29], a regional European empirical GMM [30], or several GMMs recommended for use in oceanic crustal regions ( SHARE project, [31]). ...
... Currently there exists a large collection of empirical GMMs for peak ground motions from earthquakes in shallow crustal interplate regions worldwide [1,[25][26][27]. A common trend is a deviation from self-similar scaling at larger magnitudes, in particular at near-fault distances. ...
The Icelandic strong-motion dataset is relatively small and the largest recorded earthquake magnitude is Mw 6.5, whereas events of around Mw 7.0 are known to have occurred in the South Iceland Seismic Zone (SISZ). As a result, the required features for use in probabilistic seismic hazard assessment (PSHA), such as deviation from self-similar magnitude scaling and magnitude-distance dependent saturation of ground motions at larger magnitudes, is challenging. Compounding the issue, GMMs from other seismic regions exhibit a strong bias to the available Icelandic strong-motions, underpredicting in the near-fault and overpredicting in the far-field regions. In this study, we approach this issue by considering several GMMs that have either been used or recommended for PSHA in Iceland or have functional forms that satisfy the minimum requirements of GMMs used in PSHA. We recalibrate these GMMs to fit the Icelandic data in the context of the Bayesian statistical framework and a Markov Chain Monte Carlo (MCMC) algorithm, where model inference is carried out using both non-informative and informative priors for selected model coefficients from the original GMMs. Moreover, we used a random effects model to partition the aleatory variability into inter-event and intra-event components. We show that the GMMs with informative priors for magnitude scaling and magnitude-distance scaling terms, not only capture the high near-fault amplitudes and rapid ground motion attenuation with distance, but also introduce a controlled saturation of large magnitude ground motions, which is consistent with observations in other interplate regions. In this study we also introduce a simple GMM, based on informative priors from a model for magnitude-dependent earthquake depth in the SISZ, that fully captures the salient characteristics of the recalibrated GMMs. The presented models thus form a suite of new, essentially hybrid, empirical GMMs that can be used with confidence in predicting PGA and PSA for Icelandic earthquakes, with particular implications for the reassessment of the seismic hazard of Iceland.
... Earthquakes occur on active faults, and thus the systematic mapping of active faults is a major aim of seismic hazard research (Christophersen et al., 2015;Morell et al., 2020;Styron and Pagani, 2020;Williams et al., , 2022. Within continental rifts, earthquakes on normal faults typically lead to high levels of shaking in their hanging wall basins, which are geomorphically suitable for human habitation and settlement (Bailey et al., 2000;Abrahamson et al., 2008). Consequently, normal faults inherently create conditions that lead to high seismic risk. ...
Seismic hazard assessment in slow straining regions is challenging because earthquake catalogues only record events from approximately the last 100 years, whereas earthquake recurrence times on individual faults can exceed 1000 years. Systematic mapping of active faults allows fault sources to be used within probabilistic seismic hazard assessment, which overcomes the problems of short-term earthquake records. We use Shuttle Radar Topography Mission (SRTM) data to analyse surface deformation in the Luangwa Rift in Zambia and develop the Luangwa Rift Active Fault Database (LRAFD). The LRAFD is an open-source geospatial database containing active fault traces and their attributes and is freely available at https://doi.org/10.5281/zenodo.6513691. We identified 18 faults that display evidence for Quaternary activity, and empirical relationships suggest that these faults could cause earthquakes up to Mw 8.1, which would exceed the magnitude of historically recorded events in southern Africa. On the four most prominent faults, the median height of Quaternary fault scarps varies between 12.9 ± 0.4 and 19.2 ± 0.9 m, which suggests they were formed by multiple earthquakes. Deformation is focused on the edges of the Luangwa Rift: the most prominent Quaternary fault scarps occur along the 207 km long Chipola and 142 km long Molaza faults, which are the rift border faults and the longest faults in the region. We associate the scarp on the Molaza Fault with possible surface ruptures from two 20th century earthquakes. Thus, the LRAFD reveals new insights into active faulting in southern Africa and presents a framework for evaluating future seismic hazard.
... Other GMMs that fall into these categories but fail the criteria proposed by Cotton et al. (2006) and Bommer et al. (2010) for the minimum requirement of the functional form for GMMs to be applied in PSHA are omitted. Specifically, we retain GMMs with functional forms that are able to capture the prevalent non-self-similar scaling of ground motion at large amplitudes, in particular in the near-fault region (see e.g., Abrahamson and Shedlock 1997;Halldorsson and Papageorgiou 2005;Abrahamson et al. 2008;Douglas 2018c). The final GMMs are the following: The ones calibrated in Kowsari et al. (2020b) to the Icelandic strong-motion dataset using Bayesian inference with informed priors, named as Kea20-1 to Kea20-6. ...
The earthquake hazard and seismic risk in Iceland are highest in the Southwest due to the transform faulting in the South Iceland Seismic Zone (SISZ) and Reykjanes Peninsula Oblique Rift (RPOR) being in close proximity to a large part of the population. Reliable probabilistic seismic hazard assessment (PSHA) is therefore critical in this region which in turn requires two of its key elements: the most appropriate ground motion models (GMMs) and the specification of seismic sources. In this study, we address this by employing a suite of new hybrid Bayesian empirical GMMs and a new physics-based finite-fault system model for the SISZ–RPOR. By ranking the GMMs using the deviance information criterion against the Icelandic strong-motion dataset we propose backbone GMMs (i.e., the most appropriate models), which along with their backbone Δ-factors not only comprehensively capture the characteristics of Icelandic data but also the epistemic uncertainties of their ground motion prediction. We then simulate suites of synthetic finite-fault earthquake catalogues that are consistent with the physics-based fault system and long-term seismic activity of the region. We carry out a Monte-Carlo PSHA for two representative near-fault (the town of Selfoss) and far-field (the capital city of Reykjavik) sites in Southwest Iceland, and compare the results with those of a classical PSHA. We show that the backbone PSHA is consistent with classical PSHA point estimates but more importantly, the backbone approach reveals the “body” of the hazard i.e., the majority of realistically expected hazard values, which dwarfs any differences in the results from the two approaches. The PGA results show that the body of hazard values varies from 0.07-0.13 g and 0.4-0.6 g for Reykjavik and Selfoss, respectively. The scale factor is distance- and period-dependent that results in a constant body of the backbone hazard values for a far-field site at all periods while at long periods and decreasing annual exceedance rates, the body progressively increases. Moreover, the disaggregation showed that the modal event for a 475 year return period is a Mw ~ 6–6.5 at distance ~ 14–26 km for the far-field site, but at ~ 6 km for the near-fault site. We conclude that the backbone approach and the models used in this study make ideal candidates for improved PSHA for Iceland.
... Yerel zemin özelliklerinin farklılaşması, kuvvetli yer hareketinin etkisinde bazı sahalarda yapıya gelen sismik yüklerin büyümesine, bazı sahalarda ise küçülmesine neden olabilir. Zemin büyütmesi olarak tanımlanan bu olay, üst 30 metre için zeminin ortalama kayma dalgası hızına bağlı olarak hesaplanabilen bir fonksiyondur [1]. Bu nedenle yüzeyden 30 m derinlik içinde kalan zemin tabakalarının dinamik özellikleri önemlidir. ...
The shear wave velocity (Vs) is one of the important parameters in the study of determining geotechnical engineering problems. In the dynamic field classification, the shear wave velocity is important for the first 30 meters’ depth from the surface. Therefore, the shear wave velocity (VS30) and the SPT-N value are necessary for earthquake engineering studies such as ground behavior, ground-structure interaction. The shear wave velocity of soil can be determined using seismic methods such as seismic refraction and in-downhole seismicity in the field. But, these methods are time-consuming and uneconomical methods, requiring a large workforce. For this reason, many studies use empirical approaches that calculate Vs depending on the number of SPT-N. However, these approaches have been made in different fields of study. Because the soil conditions differ, it is necessary to determine the accuracy of these approaches for the Eskisehir ground. In this study, the real Vs values determined using seismic methods within the scope of land studies in Eskişehir, and the Vs values calculated from the SPT-N values obtained from drilling operations representing the Eskişehir ground were compared. As a result, most suitable method was determined statistically.
... Since the 1906 San Francisco earthquake, seismologists have recognized that unconsolidated material with low seismic velocity could amplify shaking (e.g., Wood, 1908;Kanai and Yoshizawa, 1956;Gutenberg 1957;Borcherdt, 1970). Although site effects will modify ground-motion in more complicated ways than a GMM site term alone can capture, present models incorporate site effects using V S30 , the time-averaged shearwave velocity in the top 30 m of soil, as a proxy (Abrahamson et al., 2008;Borcherdt, 2014;Gregor et al., 2014). Although ground-motion can also be affected by factors other than local site conditions (Olsen, 2000), in the development of national hazard maps using ergodic GMMs, the effect of the complexity of the site amplification beyond V S30 is represented by the aleatory standard deviation of the GMM. ...
Prior studies have repeatedly shown that probabilistic seismic hazard maps from several different countries predict higher shaking than that observed. Previous map assessments have not, however, considered the influence of site response on hazard. Seismologists have long acknowledged the influence of near-surface geology, in particular low-impedance sediment layers, on earthquake ground-motion at frequencies of engineering concern. Although the overall effects of site response are complex, modern ground-motion models (GMMs) account for site effects using terms based on VS30, the time-averaged shear-wave velocity in the upper 30 m of the Earth’s surface. In this study, we consider general implications of incorporating site terms from modern GMMs using site-specific VS30 as a proxy in probabilistic seismic hazard maps for California. At the long periods (1–5 s) that affect tall buildings, site terms amplify the mapped hazard by factors of 1–3 at many sites relative to maps calculated for the standard reference soft-rock site condition, VS30 = 760 m/s. However, at the short periods of ground-motion that are the main contributors to peak ground acceleration (PGA) and thus affect smaller structures, only negligible effects occur due to nonlinear deamplification of strong ground-motion at high frequencies. Nonlinear deamplification increases as the shaking level increases. For very strong shaking, deamplification can overcome the linear amplification, yielding net deamplification. We explore the implications of these results for the evaluation of hazard maps. Because site effects do not change the maps appreciably at short periods, we can exclude site response as an explanation for why the maps overpredict historically observed shaking as captured by the California Historical Intensity Mapping Project (CHIMP) dataset. The results are expected to be generalizable to regions that are comparable to California in terms of structure and seismicity rates. In low-to-moderate-seismicity regions where the hazard reflects weaker shaking, nonlinear site response is expected to be less important for the hazard.
... Seismic hazard analyses on major projects are typically conducted using a probabilistic approach, whereby stochastic models are used as components in solving the hazard integral. These models, such as modern ground motion prediction equations and recurrence relationships, are generally calibrated to moment magnitude, M W [8][9][10][11][12]. However, earthquake catalogs used to develop tools for use in probabilistic seismic hazard analysis tend to have earthquakes listed with differing magnitude types, such as surface wave magnitude, M S , short-period body wave magnitude, m b , the local magnitude, M L , also commonly known as the magnitude on the Richter scale [13][14][15][16]. ...
Utilizing several international and local earthquake catalogs, a set of regression models converting magnitude types typically found in the South Korean region to moment magnitude MW is presented. These linear regressions were performed using ordinary and total least squares techniques. A standard deviation applied to the residuals was used as a metric for ranking the MW regressions. This resulted in MW regressions from MV,JMA, MD,JMA, MS,MOS, and MS,BJI having the lowest standard deviations, while ML,IDC showed the highest standard deviation. Other magnitude types ranked differently depending on regression type. An examination of the residuals showed a linear model was appropriate for most magnitude types, with the exception of ML,KMA and ML,IDC. Residuals suggested a bilinear model worked well for ML,KMA, while ML,IDC showed a monotonic trend.
... Literature reviews of several models of earthquake ground motion construction performed by Douglas andAochi (2008) andÓ lafsson et al. (2001) show that all those techniques can be categorized into three groups: (1) The deterministic approach, where the model is based on physical principles, produces ground motions by modeling those parameters that affect their shape, duration, and frequency content (e.g., Atkinson & Boore, 2007;Atkinson & Somerville, 1994;Boore, 1983Boore, , 2003Hanks, 1979;Hanks & McGuire, 1981;Pitarka et al., 1998;Silva et al., 1999). (2) The empirical or stochastic simulations are based on the assumption that future scenarios will be akin to those observed in earlier events and so try to match with target seismological and probabilistic features (e.g., Anderson, 1997;Abrahamson & Shedlock, 1997;Abrahamson et al., 2008;Baker & Cornell, 2006;Bommer & Alarcon, 2006;Campbell, 1986;Douglas, 2003;Joyner & Boore, 1988;Lee et al., 2000;Power et al., 2008;Scherbaum et al., 2004;Watson-Lamprey & Abrahamson, 2006). (3) Hybrid approaches combine factors of both (e.g., Campbell, 2003Campbell, , 2007Douglas et al., 2006;Hartzell et al., 2002;Hisada, 2008;Mai & Beroza, 2003;Pitarka et al., 2000;Scherbaum et al., 2006;Tavakoli & Pezeshk, 2005). ...
In this study, a stochastic simulation model proposed by Yamamoto and Baker (Bulletin of the Seismological Society of America 103:3044–3056, 2013) is applied to the Iranian strong motion database, which comprises more than 3828 recordings for the period between 1975 and 2018. Each ground motion is decomposed into wavelet packets. Amplitudes of wavelet packets are divided into two groups, and for each group, model parameters are estimated using the maximum likelihood method. Regression coefficients are then obtained relating model parameters to seismic characteristics such as earthquake magnitude, distance, and site condition. Inter-event residuals of coefficients and correlation of total residuals of those parameters are also calculated. An inverse wavelet packet transform is used to reconstruct the amplitudes in the time domain and perform the simulation. Finally, a validation test is performed. The comparison of ground motion intensity measures for recorded and simulated time series shows acceptable conformity in the application. The estimated parameters using the simulated data agree with the real data, indicating the acceptable validity of the estimated stochastic simulation model. The obtained regression equations can generate ground motions for future earthquake scenarios in Iran.
... For the instrumental period up to 2017, all catalogs used in hazard studies included LDG solutions, in which earthquakes are characterized by local LDG magnitude [M L , LDG 1998]. One major advantage of the LDG catalog is that it has reported the same M L since 1962; however, the ground-motion models to be used in hazard studies were first developed for surface magnitude [M S ; e.g., pan-European models by Ambraseys, 1995, Ambraseys et al., 1996, and Berge-Thierry et al., 2003, and then for moment magnitude [M W ; e.g., western US models, next generation acceleration models, Abrahamson et al., 2008, Bozorgnia et al., 2014 or European models based on the RESORCE database, Douglas et al., 2014]. Use of the LDG catalog thus implies a magnitude conversion known to be responsible for strong uncertainties. ...
This article aims to provide an overview of successive seismic zonations inmainland France and probabilistic seismic hazard studies performed over the previous ¼30 years. A short presentation is given on the engineering and regulatory framework that shapes the background of seismic zonation and hazard studies, followed by a scientific overview of published probabilistic seismic hazard estimations.
The components of these past PSHA studies are summarized (seismic source models, groundmotion models, management of uncertainties). The evolution of hazard estimates with time is displayed for a set of representative cities. Finally, three generations of official seismic zonation maps in France are presented (1967, 1986, 2004), and the evolution of methods and results is highlighted.
This review shows that the academic community has previously had little involvement in this topic. As current zonation relies on outdated models, there is an opportunity for scientific and engineering communities to efficiently work together to build the next generation of probabilistic seismic hazard models for France.
... These ergodic models tend to have large aleatory variability as they treat some of the systematic effects for a specific site/source location as random variability that can occur anywhere. Examples of models that have been developed under this approach are the NGA-West GMMs for California (Abrahamson et al. 2008), and the European GMMs derived from the RESORCE database (Douglas et al. 2014); however, as more data are collected, the ergodic assumption can be relaxed, and repeatable effects related to the source, path and site can be properly modeled, which leads to a decrease in the aleatory variability. This reduction has a large impact on the hazard at large return periods because, the ground-motion aleatory variability controls the slope of the hazard curves which has a large influence on the hazard at large return periods. ...
A new non-ergodic ground-motion model (GMM) for effective amplitude spectral (EAS) values for California is presented in this study. EAS, which is defined in Goulet et al. (Effective amplitude spectrum (eas) as a metric for ground motion modeling using fourier amplitudes, 2018), is a smoothed rotation-independent Fourier amplitude spectrum of the two horizontal components of an acceleration time history. The main motivation for developing a non-ergodic EAS GMM, rather than a spectral acceleration GMM, is that the scaling of EAS does not depend on spectral shape, and therefore, the more frequent small magnitude events can be used in the estimation of the non-ergodic terms. The model is developed using the California subset of the NGAWest2 dataset (Ancheta in PEER NGA-West2 database. Tech. rep., PEER, Berkeley, CA, 2013). The Bayless and Abrahamson (Bull Seismol Soc Am 109(5): 2088-2105, https://doi.org/10.1785/0120190077, 2019b) (BA18) ergodic EAS GMM was used as backbone to constrain the average source, path, and site scaling. The non-ergodic GMM is formulated as a Bayesian hierarchical model: the non-ergodic source and site terms are modeled as spatially varying coefficients following the approach of Landwehr et al. (Bull Seismol Soc Am 106(6):2574-2583. https://doi.org/10.1785/0120160118, 2016), and the non-ergodic path effects are captured by the cell-specific anelastic attenuation attenuation following the approach of Dawood and Rodriguez-Marek (Bull Seismol Soc Am 103(2B):1360-1372, https://doi.org/10.1785/0120120125, 2013). Close to stations and past events, the mean values of the non-ergodic terms deviate from zero to capture the systematic effects and their epistemic uncertainty is small. In areas with sparse data, the epistemic uncertainty of the non-ergodic terms is large, as the systematic effects cannot be determined. The non-ergodic total aleatory standard deviation is approximately 30 to \(40\%\) smaller than the total aleatory standard deviation of BA18. This reduction in the aleatory variability has a significant impact on hazard calculations at large return periods. The epistemic uncertainty of the ground motion predictions is small in areas close to stations and past events.
... Models developed under this assumption tend to have stable median estimates but large aleatory variability. Some models developed with the ergodic approach are: the NGA West GMMs for California Abrahamson et al. (2008), and the Douglas et al. (2014) GMM for Europe. Non-ergodic GMMs recognize that source, path, and site effects are systematically different at different parts of the world and account for these differences in the model development. ...
A new approach for creating a non-ergodic $PSA$ ground-motion model (GMM) is presented which account for the magnitude dependence of the non-ergodic effects. In this approach, the average $PSA$ scaling is controlled by an ergodic $PSA$ GMM, and the non-ergodic effects are captured with non-ergodic $PSA$ factors, which are the adjustment that needs to be applied to an ergodic $PSA$ GMM to incorporate the non-ergodic effects. The non-ergodic $PSA$ factors are based on $EAS$ non-ergodic effects and are converted to $PSA$ through Random Vibration Theory (RVT). The advantage of this approach is that it better captures the non-ergodic source, path, and site effects through the small magnitude earthquakes. Due to the linear properties of Fourier Transform, the $EAS$ non-ergodic effects of the small events can be applied directly to the large magnitude events. This is not the case for $PSA$, as response spectrum is controlled by a range of frequencies, making $PSA$ non-ergodic effects depended on the spectral shape which is magnitude dependent. Two $PSA$ non-ergodic GMMs are derived using the ASK14 and CY14 GMMs as backbone models, respectively. The non-ergodic $EAS$ effects are estimated with the LAK21 GMM. The RVT calculations are performed with the V75 peak factor model, the $D_{a0.05-0.85}$ estimate of AS96 for the ground-motion duration, and BT15 oscillator-duration model. The California subset of the NGAWest2 database is used for both models. The total aleatory standard deviation of the two non-ergodic $PSA$ GMMs is approximately $30$ to $35\%$ smaller than the total aleatory standard deviation of the corresponding ergodic $PSA$ GMMs. This reduction has a significant impact on hazard calculations at large return periods. In remote areas, far from stations and past events, the reduction of aleatory variability is accompanied by an increase of epistemic uncertainty.
... The time-averaged shear-wave velocity (V S ) in the upper 30 m depth from the ground surface, or V S30 , has been found to correlate with seismic site amplification (Boore et al., 1993;Borcherdt, 1994;Borcherdt, 2012) and is often used as a predictor to describe local site effects in ground-motion models (Abrahamson and Shedlock, 1997;Abrahamson et al., 2008;Kamai et al., 2016). V S30 is also used as the basis for demarcating seismic site classes in building codes (Building Seismic Safety Council (BSSC), 2003;Eurocode 8, 2004) and hazard assessment products (Wald et al., 1999(Wald et al., , 2008. ...
The time-averaged shear-wave velocity in the upper 30 m depth from the ground surface, or VS30, is often used as a predictor to describe local site effects in ground-motion models. Although VS30 is typically determined from in situ measurements, it is not always feasible to obtain such measurements due to project restrictions or site accessibility. This motivates the development and use of proxy-based VS30 predictions that leverage more readily available secondary information such as surface geology, topographic slope, or geomorphic terrain classes to estimate the mean VS30 and associated uncertainty. Traditionally, empirical distributions of VS30 have been observed to have long right tails, leading to high levels of associated uncertainty. In this study, we present a physical framework that is grounded in fundamental principles of geostatistics and probability to explain the uncertainty and skewness associated with VS30 measurements. Specifically, by invoking Lyapunov’s central limit theorem, we hypothesize that the distribution of VS30 can be theoretically approximated by a reciprocal–normal distribution. We show that a non-normal and skewed distribution of VS30 is to be expected and is not a sign of measurement error or sampling bias, although sampling bias can exaggerate such skewness. Our framework also enables us to propose the mode as a characteristic value of VS30 measurements, as opposed to the mean or median, which can overestimate the most probable value.
... Other building codes worldwide also choose it as the basis for specifying site categories (Eurocode 8, 2004; American Society of Civil Engineers [ASCE], 2010). V S30 is also used as an explanatory variable for site effects in ground-motion prediction equations (GMPEs; Abrahamson et al., 2008;Chiou and Youngs, 2008). The applications of V S30 in these fundamental areas in turn lead to a wealth of studies supporting its use (Kamai et al., 2016;Liu et al., 2017), including its application in China (Li et al., 2019;Wu et al., 2020). ...
Employing extrapolation models to estimate the time-averaged shear-wave velocity to 30 m (VS30) from a shallow borehole profile is an effective way to expand the VS30 data volume and a necessary initial step for developing VS30 proxy models. Past extrapolation model studies have relied only on shallow borehole shear-wave velocity (VS) profiles to estimate VS30. In this study, we enhance the model by accounting for additional parameters including location slope, geologic age, and geotechnical class. We first compile a new borehole profile database (BPDB) that contains information about 8831 boreholes in China. Using this BPDB, we analyze the VS characteristics of strata for various location slopes, geologic ages, and geotechnical classes. The result shows that the location slope and geologic age have significantly different effects on the VS characteristics, whereas the differences for sand, silt, and clay are small. We build a parameter classification scheme that classifies the location slope into six groups, the geologic age into seven hierarchical types, and the geotechnical class into four hierarchical types. This scheme ensures that each group/type has its distinctive VS characteristic. We evaluate five existing VS models and choose the model that shows the best performance on the BPDB as the “prototype” model. We classify the BPDB boreholes by the parameter classification scheme and use the form of “prototype” model to develop a parametrical model that consists of 33 single-parameter-value models. For a shallow borehole (<30 m), if its location slope, geologic age, or geotechnical class is available besides its VS profile, applying the parametrical model will get more accurate estimated VS30 and model uncertainty estimation than those of existing models that only utilize the information of the VS profile.
... More comprehensive literature reviews can be found elsewhere. 5,6 By the mid-2000s, various key areas in earthquake engineering and seismology began to mature-namely, Ground Motion Prediction Equations (GMPEs), 7 Probabilistic Seismic Hazard Analysis (PSHA), 8 and Performance-Based Earthquake Engineering 20 -and seismic fragility characterization began to take center stage. It was around the same time that it was recognized-and explored in recurrent iterations-that ground motion selection and scaling with a single intensity measure may have shortcomings. ...
Ground motion selection is arguably the most crucial step in performance-based seismic design and risk assessment, as it bears the highest level of uncertainty that needs to be propagated through the calculations. The presently typical approach to capture this uncertainty in predicted structural responses is to use a suite of ground motions that match a uniform-hazard response spectrum. This study examines the downstream effects of ground motion selection made through a variety of conditioning criteria based on one, two, or average of more-than-two intensity measures, and also with respect to different earthquake characteristics. Ductile and nonductile reinforced concrete moment frames with varying heights are used as model problems in detailed parametric studies. A risk-based approach is adopted to develop a point-of-comparison reference demand. Seismic responses obtained using different ground motion suites compiled using three different conditioning criteria are then compared against this reference to determine the extent to which the selected ground motion suites can capture various critical structural responses.
... Cho đến thời điểm hiện tại tất cả các mô hình suy giảm dao động nền này đều đã tính đến các yếu tố hiệu ứng nền đất, kiểu đứt gãy, cánh treo đứt gãy, độ sâu đến bề mặt phá hủy động đất, bề dày tầng trầm tích,… Các mô hình suy giảm dao động nền được xây dựng trong chương trình NGA tương đối tương đồng nhau và cho kết quả phù hợp với tập hợp số liệu thực tế sử dụng [16]. Trong số các mô hình suy giảm dao động nền của chương trình NGA, mô hình suy giảm dao động nền của Campbell và Bozorgnia (2014) [13] được xây dựng dựa trên cơ sở hoàn thiện các nghiên cứu của Campbell (1997) [17] và Campbell và Bozorgnia (2003, 2008 [18,19]. Đây là chuỗi mô hình suy giảm dao động nền được sử dụng phổ biến ở Việt Nam và được đánh giá là phù hợp nhất đối với điều kiện địa chấn kiến tạo của Việt Nam. ...
... Although we did not use the method of site amplification evaluation based on the time-averaged S-wave velocity of the top 30 m (V S30 ), we calculated the V S30 of each site for reference, because this parameter was commonly used in the siteeffect studies (e.g., Borcherdt, 1994;Abrahamson et al., 2008;Zhao and Xu, 2013;Gregor et al., 2014;Kamai et al., 2016). Figure 13 demonstrates the distribution of V S30 in the target area. ...
In this study, we conducted a series of microtremor surveys to understand the contribution of soil amplifications to the heavy structural damage of wooden houses in downtown Mashiki, Kumamoto, Japan, during the 2016 Kumamoto earthquake. We analyzed the microtremor horizontal-to-vertical spectral ratios (MHVRs) of each observation site. A few previous studies have demonstrated the applicability of the earthquake horizontal-to-vertical spectral ratios (EHVRs) to identify velocity structures. Therefore, we transformed the MHVRs into pseudo-EHVRs (pEHVRs) using the EHVR-to-MHVR ratio (EMR) method. We identified the velocity structures in Mashiki, according to the diffuse field concept (DFC) for earthquake, using the pEHVRs. We also estimated the seismological bedrock motions during the mainshock based on the DFC. We then performed the seismic ground response analyses of subsurface structures, using a 1D linear analysis and an equivalent linear analysis (ELA). Finally, we obtained the distribution maps of peak ground acceleration (PGA) and peak ground velocity (PGV) for Mashiki town. We obtained the following results: (a) the thickness of the soft sediment under the southwestern part of Mashiki is deeper than that under the northeastern part; (b) the thickness of the soft sediments was a primary cause of the heavy damage to buildings of Mashiki; (c) the ground motions estimated by the ELA method seemed to be close to the observed seismic ground motions in Mashiki; (d) the distribution of the estimated PGV in Mashiki had a close relationship with the damage ratio distribution of buildings; (e) the EMR method, along with the DFC for earthquake and the 1D ELA method, successfully simulated the strong motions that occurred during the mainshock in Mashiki.
... For other regions in Iceland however where the modal event of the disaggregated seismic hazard is a larger magnitude earthquake, we need reliable and physical consistent strong-motion prediction models, in particular for near-fault sites. In that context we note that empirical GMMs for shallow crustal earthquakes in interplate tectonic regions limit the predicted ground motions from larger magnitude earthquakes, particularly in the near-fault region through a quadratic magnitudeterm and/or magnitude-distance-dependent terms [111,[123][124][125]. However, the non-ergodic GMMs for Iceland do not allow for such non-self similar ground motion scaling with magnitude, and as a result there is reason to doubt their ground motion predictions at larger magnitudes. ...
Earthquake ground motion prediction in Iceland where strong-motion data is scarce poses a challenge as empirical ground motion models (GMM) developed from data in other regions systematically fail to capture the consistently large near-fault peak amplitudes and their rapid attenuation with distance from the earthquake source. Therefore, regional GMMs must be constructed but due to the limited data, and none above Mw6.5, earthquake source scaling is unconstrained at larger magnitudes. Instead, physics-based GMMs should be applied based on realistic earthquake source modeling. For that purpose, a seismological model constructed around the specific barrier model (SBM) has been calibrated in the context of the stochastic method using random vibration theory, to earthquake high-frequency strong-motions in the South Iceland Seismic Zone. The SBM is used as it provides a physically consistent and efficient description of the heterogeneous faulting processes that are responsible for the generation of high-frequency waves. On the basis of the concise point-source representation of radiated spectra from N subevents of the SBM the pseudo-spectral accelerations were modeled and compared with that of data in the spectral domain. Backwards model selection was then carried out using Bayesian inference with Monte Carlo simulations and Markov Chains. The number of parameters in the model inference was reduced to obtain stable Markov chains and posterior probability density functions for each parameter, eliminating parametric cross-correlations to the extent possible. The seismological model has been shown to be unbiased with respect to strong-motions in the SISZ, with a total standard deviation of 0.216 (common logarithm), with only a minor contribution from inter-event variability, suggesting a relatively uniform character of SISZ earthquake strong-motions. We showcase the application of the SBM extended into a finite-fault and model the three Mw6.3-6.5 earthquakes in the dataset, allowing subevents of varying sizes to populate the fault plane and provide a more realistic earthquake source and acceleration ground motion time history modeling. The time domain results are shown to capture the essential characteristics of the ground motions of the three largest earthquakes in the dataset. We present therefore the SBM as a physically consistent source model of SISZ earthquakes for the generation of synthetic strong-motion time histories or peak parameters, with potential applications in scenario simulations and probabilistic or deterministic seismic hazard assessment.
... To provide a concrete example of this point, consider the magnitude scaling of the Next Generation Attenuation-West (NGA-West) models (the main points here relate to the parameterization of both the NGA-West1 and NGA-West2 models; Abrahamson et al., 2008;Gregor et al., 2014). Following the work of Fukushima (1996) and using the basic concept of an earthquake source spectrum with at least one corner frequency that scales with magnitude, such as the omega-squared spectrum (Aki, 1967), it can be shown that the magnitude scaling of response spectral ordinates should behave as in Figure 6. ...
Capturing the center, the body, and the range of ground-motion predictions is an indispensable element of site-specific probabilistic seismic hazard analyses (PSHAs), for which the logic tree is the ubiquitous tool in current practice. The criteria for selecting the ground-motion models (GMMs) used in such studies have generally been focused on their potential applicability to the region and site for which the PSHA is being conducted. However, except for applications within the few regions with abundant ground-motion databases, it will rarely be the case that GMMs can be identified, which are perfectly calibrated to the characteristics of the target study region in terms of source and path properties. A good match between the generic site amplification model within the GMM and the site-specific dynamic response characteristics is equally, if not more, unlikely. Consequently, adjustments are likely to be made to the selected GMMs to render them more applicable to the target region and site. Empirical adjustments for host-to-target-region source differences using local recordings are unlikely to be robust, unless these have been generated by earthquakes from a wide range of magnitudes. Empirical adjustments for site characteristics are impossible, unless there are recordings from the target site. Therefore, the preferred approach makes parametric adjustments to empirical GMMs, isolating each host-to-target difference to map the individual contributions to the epistemic uncertainty. For such an approach to be applied, the emphasis moves from selecting GMMs on the basis of their applicability to focusing on their amenability to being adjusted to the target region and site. An adaptable equation is characterized by well-constrained host-region source, path, and site characteristics and a functional form in which response spectral accelerations scale with source, path, and site characteristics in a manner similar to the scaling implicit in stochastic simulations based on Fourier amplitude spectra.
... Current building codes use the average shear wave velocity in the top-most 30 m (V S30 ) as a proxy to classify soil sites and account for the effects of the local soil conditions on the seismic action [7,8]. V S30 is also commonly implemented in ground motion prediction equations to consider expected soil amplifications [9][10][11]. Recently proposed classification schemes have further suggested the use of the average shear wave velocity over the top-most z meters (V SZ ), alongside other geotechnical parameters, for seismic zonation purposes (e.g., [12][13][14][15]). ...
The shear wave velocity profile is of primary interest for geological characterization of soil sites and elucidation of near-surface structures. Multichannel Analysis of Surface Waves (MASW) is a seismic exploration method for determination of near-surface shear wave velocity profiles by analyzing Rayleigh wave propagation over a wide range of wavelengths. The inverse problem faced during the application of MASW involves finding one or more layered soil models whose theoretical dispersion curves match the observed dispersion characteristics. A set of open-source MATLAB-based tools for acquiring and analyzing MASW field data, MASWaves, has been under development in recent years. In this paper, a new tool, using an efficient Monte Carlo search technique, is introduced to conduct the inversion analysis in order to provide the shear wave velocity profile. The performance and applicability of the inversion scheme is demonstrated with synthetic datasets and field data acquired at a well-characterized geotechnical research site.
... Several modern ground motion attenuation equations (e.g., new generation attenuation models, NGA) allow the recognition of the between-earthquake correlation, because the equations include specifications of the between-earthquake and within-earthquake components of variability (Boore et al. 1997;Douglas 2003Douglas , 2006Tsai et al. 2006;Abrahamson et al. 2008). The site-to-site correlation should be empirically evaluated for a given area. ...
The construction of nuclear power plants in China has proceeded rapidly in recent years, and a nuclear power plant cluster is present in the coastal area of Fujian Province. Considering the lessons of the Fukushima Daiichi nuclear power plant accident, we applied the Monte Carlo approach to calculate the correlation characteristics of earthquake impacts on the nuclear power plant cluster and to assess the seismic hazards at multiple sites. Based on the seismic source zone model, seismicity model and ground-motion prediction model of the Seismic Ground Motion Parameters Zonation Map of China, many earthquake scenarios were sampled, and the possibility of multiple sites experiencing ground motions that exceed critical values at the same time were obtained. The results show that the correlation between nuclear power plants Fuqing (C) and Putian (D) is the largest and that they have a slight probability of exceeding their respective design criteria at the same time. The correlation of earthquake impacts on nuclear power plants Ningde (A) and Xiapu (B) is also high, but the probability that they simultaneously exceed their respective design criteria is very low. This study can provide a reference for the site selection of nuclear power plants.
... In addition, comparisons of crustal GMMs from the NGA-West1 project (Abrahamson et al., 2008), the NGA-West2 project (Gregor et al., 2014), and the pan-European project (Campbell, 2016;Douglas et al., 2014) show a marked decrease in MSR at M ' 6:5 À 7:0 for all spectral periods, although MSR is relatively steeper at longer periods. Some of these GMMs even predict near-zero MSRs at very close distances to the rupture surface for the larger events. ...
In this article, I propose a method for estimating the magnitude [Formula: see text] at which subduction megathrust earthquakes are expected to exhibit a break in magnitude scaling of both seismic source dimensions and earthquake ground motions. The methodology is demonstrated by applying it to 79 global subduction zones defined in the literature, including Cascadia. Breakpoint magnitude is estimated from seismogenic interface widths, empirical source scaling relations, and aspect ratios of physically unbounded earthquake ruptures and their uncertainties. The concept stems from the well-established observation that source-dimension and ground motion scaling decreases for shallow continental (primarily strike-slip) earthquakes when rupture exceeds the seismogenic width of the fault. Although a scaling break for megathrust earthquakes is difficult to observe empirically, all of the instrumentally recorded historical [Formula: see text] mega-earthquakes have occurred on subduction zones with [Formula: see text] (8.1–8.9), consistent with an observed break in source scaling relations derived from these same events. The breakpoint magnitudes derived in this study can be used to constrain the magnitude at which the scaling of ground motion is expected to decrease in subduction ground motion prediction equations.
... Empirical ground motion prediction equations (GMPEs) have been widely used for probabilistic seismic hazard analysis (PSHA) because they are directly constrained by the observed data (Abrahamson et al. 2008). Bommer and Abrahamson (2006) noted that GMPE controls the shapes of the seismic hazard curves and has a significant impact on PSHA. ...
Ground motion prediction is an important element in seismic hazard analysis. However, the availability of recorded strong ground motion data is limited, particularly for large events in near-source regions. Recently, several physics-based ground motion simulation approaches have been developed, which may be useful for understanding the effect of earthquake source on near-source ground motion characteristics. In this study, we investigated the sensitivity of near-source ground motions to finite earthquake source processes with pseudo-dynamic source models, based on 1-point and 2-point statistics of earthquake source parameters. We simulated ground motions for Mw 6.6 and 7.0 vertical strike-slip events using pseudo-dynamic source models derived from multiple sets of input source statistics and investigated the characteristics of near-source ground motions relative to the input source statistics, focusing on the relative station locations with respect to finite-fault geometry. Our results show that the effect of earthquake source on near-source ground motions can vary depending on the locations of near-source stations. The variability of ground motion intensities derived from multiple sets of input source statistics was greater in the forward directivity region. This pattern is also consistent for pseudo-spectral accelerations with various periods. The pseudo-dynamic source modeling method with 1-point and 2-point statistics seems to be an efficient framework for understanding the effect of earthquake source on near-source ground motion characteristics.
... Taking into account COV% of 5-10% for shear wave velocity of soil, the COV% of the T s can be presumed between 5 and 10%, respectively. Regarding the Abrahamson et al. (2008) attenuation law and using MCS simulation method for motions with 5.5-8 magnitude with distance of 50 km, correlation coefficient value between PGA and M of 0.55 is calculated. ...
Seismic coefficient values coupled with minimum pseudo-static safety factors are still used for analysis, where selection of seismic coefficients relies on expertise and judgment. However, safety factor approach does not give any idea about the deformations and displacements that are expected to occur during earthquake loading. Displacements are mostly evaluated by equations based on yield acceleration of the slope and maximum acceleration of sliding mass. In deterministic calculation, input information is considered as constant amounts as in cohesion, internal friction angle, slope and other characteristics. Due to the fact that co-seismic slopes deformation is a function of seismic yield coefficient (ky) and other effective parameters, with the use of statistical analysis, the statistical distribution and standard deviation of ky can be calculated. In the current state of the art, in order to study the changes in slope reliability the following steps were taken: analyzing the pseudo-static of slope and other factors having different mechanical and physical parameters, determining the relationship between seismic yield coefficient of slopes and other parameters with the use of genetic algorithm and revolutionary algorithm, simulation of the factors effective on ky with specific statistical distribution applying Monte Carlo simulation using random number generator, determining statistic distribution and standard deviation of seismic yield coefficient of slope and finally determining the slopes failure probability based on allowable co-seismic slope displacement.
... As a result, many researchers have expanded efforts to develop more physically justified empirical GMMs, with the hopes of decreasing the associated standard deviation. However, using more complicated functional forms of GMMs over the last decades [31][32][33][34][35] has not led to the expected decrease in the total variability. On this note, the investigation of the main sources and physical understanding of uncertainties associated with GMMs is a challenging research topic that has important implications for the seismic capacity of critical structures [8,[36][37][38]. ...
Earthquake recordings on two small-aperture (covering ∼ 1.2km2 each) strong-motion arrays in Iceland (ICEARRAY I and II) exhibit considerable variations in the spatial distribution of ground-motion amplitudes. To better understand this spatial variability, we use a Bayesian Hierarchical Model (BHM) that incorporates ground motions models (GMMs) for peak ground accelerations (PGA) developed from ground motion databases recorded by the two arrays, respectively. The posterior distributions of the model parameters are then determined using Markov Chain Monte Carlo simulations in the context of Bayesian statistical methods. The BHM allows the partitioning of a GMM into event, station, and event-station terms, which in turn allows the relative contributions of source, path, and site effects to be quantified. The results indicate that site effects can dominate the spatial distribution of ground-motion parameters (e.g., PGA) observed across both ICEARRAY I and II. Although the site conditions across ICEARRAY I have been classified as uniform (i.e.,“rock”with a relatively flat topography), station terms contribute∼13%to the total variability in the amplitudes of predicted ground motions across the array. In contrast to ICEARRAY I, the variation of the geologic profiles and topography is much greater across ICEARRAY II. As a result, the inter-station variability is shown to contribute up to∼57%of the total variability in the amplitudes of predicted ground motions across the array, with the contributions being less constrained for ICEARRAY II than ICEARRAY I due to the relative sizes of the recorded ground motion databases.These results facilitate our understanding of the key factors that affect the variation of seismic ground motions across a relatively small area. Such a detailed microzonation is of great importance for earthquake hazard assessment on a local scale and has practical implications for engineering decision making.
... This choice for the IM definition follows standards adopted in many similar studies(Iervolino et al. 2010a; Galasso and Iervolino 2011) though evidently the results of the validation study are somewhat impacted by this selection. The median and dispersion for the target IMs are given for each Ti as the average of four GMPEs used in the Western US, namely the ones by Campbell and Bozorgnia,Abrahamson and Silva, Boore and Atkinson, and Chiou and Youngs (Abrahamson et al. 2008;Power et al. 2008). Note that this is simply chosen for consistency with previous work of the authors; any other GMPEs, or any other approach that would define an IM description to match(Bradley 2010;Lin et al. 2013), could have been used instead. ...
An important consideration for the adoption of stochastic ground motion models in performance-based earthquake engineering applications is that the probability distribution of target intensity measures from the developed suites of time-histories is compatible with the prescribed hazard at the site and structure of interest. The authors have recently developed a computationally efficient framework to modify existing stochastic ground motion models to facilitate such a compatibility. This paper extends this effort through a validation study by comparing the seismic demand of recorded ground motions to the demand of stochastic ground motion models established through the proposed modification. Suites of recorded and stochastic ground motions, whose spectral acceleration statistics match the mean and variance of target spectra within a period range of interest, are utilized as input to perform response history analysis of inelastic single-degree-of-freedom (SDoF) case-study systems. SDoF systems with peak-oriented hysteretic behavior, strain hardening, and (potentially) degrading characteristics, experiencing different degree of inelastic response, are considered. Response is evaluated using the peak inelastic displacement and the hysteretic energy given by the work of the SDoF restoring force as engineering demand parameters (EDPs). The resultant EDP distributions are compared to assess the effect of (and validate) the proposed modification. It is shown that the proposed modification of stochastic ground motion models can provide results that are similar to these from recorded ground motion suites, improving any (in some cases large) discrepancies that exist for the initial, unmodified stochastic ground motion model.
... Figure 1a shows that both the Shahi and Baker (2011) and adopted approaches result in similar SA distributions, with some negligible differences in the lower or upper tails of the distribution. Such differences are practically not significant when compared to the difference in ground motion estimations from different GMMs themselves (Abrahamson et al. 2008, Bozorgnia et al. 2014). Figure 1b also shows the 16 th , 50 th , and 84 th percentile spectra for a range of periods from the same scenario presented. ...
This paper focuses on the selection of ground motions for seismic response analysis in the near-fault region, where directivity effects are significant. An approach is presented to consider forward directivity velocity pulse effects in seismic hazard analysis without separate hazard calculations for 'pulse-like' and 'non-pulse-like' ground motions, resulting in a single target hazard (at the site of interest) for ground motion selection. The ability of ground motion selection methods to appropriately select records which exhibit pulse-like ground motions in the near-fault region is then examined. Applications for scenario and probabilistic seismic hazard analysis cases are examined through computation of conditional seismic demand distributions and the seismic demand hazard. It is shown that ground motion selection based on an appropriate set of intensity measures (IMs) will lead to ground motion ensembles with an appropriate representation of the directivity-included target hazard in terms of IMs, which are themselves affected by directivity pulse effects. This alleviates the need to specify the proportion of pulse-like motions and their pulse periods a priori as strict criteria for ground motion selection.
Seismic hazard and risk analyses underpin the loadings prescribed by engineering design codes, the decisions by asset owners to retrofit structures, the pricing of insurance policies, and many other activities. This is a comprehensive overview of the principles and procedures behind seismic hazard and risk analysis. It enables readers to understand best practises and future research directions. Early chapters cover the essential elements and concepts of seismic hazard and risk analysis, while later chapters shift focus to more advanced topics. Each chapter includes worked examples and problem sets for which full solutions are provided online. Appendices provide relevant background in probability and statistics. Computer codes are also available online to help replicate specific calculations and demonstrate the implementation of various methods. This is a valuable reference for upper level students and practitioners in civil engineering, and earth scientists interested in engineering seismology.
We address the relation between seismic local amplification and topographical and geological indicators describing the site morphology. We focus on parameters that can be derived from layers of diffuse information (e.g., digital elevation models, geological maps) and do not require in situ surveys; we term these parameters as “indirect” proxies, as opposed to “direct” indicators (e.g., f0, VS30) derived from field measurements. We first compiled an extensive database of indirect parameters covering 142 and 637 instrumented sites in Switzerland and Japan, respectively; we collected topographical indicators at various spatial extents and focused on shared features in the geological descriptions of the two countries. We paired this proxy database with a companion dataset of site amplification factors at 10 frequencies within 0.5–20 Hz, empirically measured at the same Swiss and Japanese stations. We then assessed the robustness of the correlation between individual site-condition indicators and local response by means of statistical analyses; we also compared the proxy-site amplification relations at Swiss versus Japanese sites. Finally, we tested the prediction of site amplification by feeding ensembles of indirect parameters to a neural network (NN) structure. The main results are: (1) indirect indicators show higher correlation with site amplification in the low-frequency range (0.5–3.33 Hz); (2) topographical parameters primarily relate to local response not because of topographical amplification effects but because topographical features correspond to the properties of the subsurface, hence to stratigraphic amplification; (3) large-scale topographical indicators relate to low-frequency response, smaller-scale to higher-frequency response; (4) site amplification versus indirect proxy relations show a more marked regional variability when compared with direct indicators; and (5) the NN-based prediction of site response is the best achieved in the 1.67–5 Hz band, with both geological and topographical proxies provided as input; topographical indicators alone perform better than geological parameters.
Several devastations caused due to the earthquakes among other natural hazards and the local site conditions have a predominant influence on site amplification during the earthquake. The travel-time of average S-wave or shear wave velocity (Vs) to top 30 meters (V s 30) depth from the surface level is an extensively used parameter to predict the local site potential for amplification during the earthquakes. In the present study, the Vs profile was developed for the Amaravati region and the site has been classified according to the NEHRP and Eurocode 8. The response of the ground is characterized through equivalent linear ground response analysis using DEEPSOIL with four different input motions to mimic earthquake hazard scenarios in this region. The response spectra analysis was carried out to the soil profile of the average minimum V s 30. Peak Ground Acceleration (PGA) obtained at the free field using all selected input motions and the values of PGA are varying from 0.27 g to 0.29 g. The spatial variation of amplitude and response spectra has been observed between the free field and rock outcrop motion. Based on the V s 30 profile, the region has been classified as class "D" according to NEHRP site classification and ground-type "C" by EC-8.
In this study, a stochastic simulation model proposed by Yamamoto and Baker (2013), is applied to Iranian strong motion database which comprises more than 3828 recordings for a time period between 1975–2018. Each ground motion is decomposed into wavelet packets. Amplitudes of wavelet packets are divided into two groups and for each group model parameters are estimated using the maximum likelihood method. Regression coefficients are then obtained relating model parameters to seismic characteristics such as earthquake magnitude, distance, and site condition. Inter-event residuals of coefficients and correlation of total residuals of those parameters are also calculated. To reconstruct the amplitudes in time domain and do the simulation, inverse wavelet packet transform is used. Finally, a validation test is performed. The comparison of ground motion intensity measures for recorded and simulated time series shows an acceptable conformity in the application. The estimated parameters using the simulated data are in good agreement with the real data, indicating the acceptable validity of the estimated stochastic simulation model. Obtained regression equations can be used to generate ground motions for the future earthquake scenarios in Iran.
This paper presents new techniques for quantifying nonstationary spatial variations in strong ground motion, using data from recent well‐recorded earthquakes in New Zealand. The data set is unique in that many recording stations are relatively densely spaced, and multiple strong ground motions have been recorded at the same stations. This allows calculation of site‐specific and region‐specific correlations in ground‐motion amplitude for Wellington and Christchurch, and the results are compared to a model assuming stationary correlations at all locations. Strong nonstationarity in spatial correlation is observed in the Wellington and Christchurch regions. Heterogeneous geologic conditions appear to be associated with the nonstationary spatial correlation. Several factors influencing nonstationary spatial correlation were studied: (a) site‐specific residuals indicate deviation of correlation from a stationary model; (b) most earthquakes have no systematic effect on spatial correlations and there is no indication of a trend in correlations with magnitude; (c) rupture complexity is related to the variation of spatial correlations in ground‐motion residuals; (d) variation of site‐specific correlations cannot be resolved by using terms in Ground‐Motion Models. The nonstationary correlation approach provides an opportunity to incorporate the site‐specific effects in future correlation models.
Liquefaction assessments for tailings facilities have significant uncertainty, yet their results are typically presented as single-value deterministic factors of safety (FoSs) to compare against standard practice guidance. Some of the uncertainty is due to inherent material variability or measurement error associated with in situ testing techniques. There is also a considerable – and often ignored – contribution from the transformation models used to convert in situ measurements to design parameters. For seismic liquefaction assessments, the key sources of transformation model uncertainty are from the empirical relationships relating standard penetration testing or cone penetration testing (CPT) results to cyclic resistance and residual undrained strength. While the uncertainties associated with the material variability and measurement error will vary by site and can usually be reduced through additional investigation, the model uncertainties are constant and irreducible without further work. This paper shows how the transformation model uncertainties associated with CPT-based liquefaction assessments can be incorporated into design practice to estimate probabilities of failure and lead to very different outcomes than simply considering FoS alone.
Surface wave methods have been extensively employed to estimate time-averaged shear-wave velocity (Vs) to 30 m (Vs,30) for seismic site classification. However, the inversion of surface wave dispersion data for Vs profiling is inherently computationally intensive. To overcome the challenge involved in surface-wave inversion, a new method is proposed to directly estimate Vs,30 from surface wave fundamental-mode dispersion data without inversion. The new method is based on the concept that the phase velocity of surface waves (VR) at a given frequency (f) is proportional to the average shear-wave velocity of soils within one-half of the wavelength (λ=VR/f). The proposed method starts from calculating the Vs of the top layer as it can be directly estimated from the phase velocity of surface waves whose half wavelengths are smaller than the thickness of the top layer. Likewise, the Vs of the second layer can be deduced from the top layer Vs along with the phase velocity of surface waves whose half wavelengths are within the thickness range of the second layer. Through such a repetition of sequence-deduction, the Vss of the other layers can be calculated. This method is verified with five case studies that cover typical geotechnical sites. Results indicate that the proposed method can obtain a similar Vs,30 with the same site classification for seismic design in comparison with invasive tests and inversion techniques.
Given the deficiency of recorded strong ground-motion data, it is important to understand the effects of earthquake rupture processes on near-source ground-motion characteristics and to develop physics-based ground-motion simulation methods for advanced seismic hazard assessments. Recently, the interfrequency correlation of ground motions has become an important element of ground-motion predictions. We investigate the effect of pseudodynamic source models on the interfrequency correlation of ground motions by simulating a number of ground-motion waveforms for the 1994 Northridge, California, earthquake, using the Southern California Earthquake Center Broadband Platform. We find that the cross correlation between earthquake source parameters in pseudodynamic source models significantly affects the interfrequency correlation of ground motions in the frequency around 0.5 Hz, whereas its effect is not visible in the other frequency ranges. Our understanding of the effects of earthquake sources on the characteristics of near-source ground motions, particularly the interfrequency correlation, may help develop advanced physics-based ground-motion simulation methods for advanced seismic hazard and risk assessments.
We address the relation between local amplification and site-condition indicators derived from in situ geophysical surveys for the estimation of the VS profile, and single-station recordings processed with horizontal-to-vertical spectral ratio technique. Site-condition indicators, or proxies (e.g., VS30), aim at “summarizing” the description of the local geophysical structure, with a focus on its relation to site amplification.
The premise for our work was the compilation of two companion databases: one of soil condition proxies and the other of empirically derived Fourier amplification functions, for Swiss and Japanese stations.
We investigated the connection between these two datasets, at first, with a systematic set of regressions correlating each proxy to amplification factors within the frequency band 0.5–20 Hz, second, with a neural network (NN) structure predicting site amplification from proxies.
The regression analyses showed that, generally, site-condition parameters (SCPs) bear a better correlation with amplification within 1.7–6.7 Hz; the “best” indicators are the frequency-dependent quarter-wavelength (QWL) velocity and, among scalar parameters, VS30, the bedrock depth, and f0. Collating Swiss and Japanese datasets, the trend of variation of amplification with respect to most proxies is similar. Finally, we evaluated the prediction performance of various combinations of SCPs, for local amplification, using a NN. To attain a database large enough to constrain the estimation of the network parameters, we merged Swiss and Japanese stations into a single training and validation dataset, motivated by the similarities observed in the regression analyses. The outcome we obtained from the NN is encouraging and consistent with the results of the regressions; SCPs with higher correlation to amplification provide a better forecast of the latter (particularly within 1.7–6.7 Hz). More complete input information, such as QWL parameters (velocity, impedance contrast), or extended ensembles of scalar proxies (particularly, including f0), offer a better estimation of local amplification.
Thrust-fault earthquakes are particularly hazardous in that they produce stronger ground motion than normal or strike-slip events of the same magnitude due to a combination of hanging-wall effects, vertical asymmetry, and higher stress drop due to compression. In addition, vertical surface displacement occurs in both blind-thrust and emergent thrust ruptures, and can potentially damage lifelines and infrastructure. Our 3D dynamic rupture modeling parameter study focuses on planar thrust faults of varying dip angles, and burial depth establishes a physics-based understanding of how ground motion and permanent ground surface displacement depend on these geometrical parameters. We vary dip angles from 20° to 70° and burial depths from 0 to 5 km. We conduct rupture models on these geometries embedded in a homogeneous half-space, using different stress drops but fixed frictional parameters, and with homogeneous initial stresses versus stresses tapered toward the ground surface. Ground motions decrease as we bury the fault under homogeneous initial stresses. In contrast, under tapered initial stresses, ground motions increase in blind-thrust faults as we bury the fault, but are still the highest in emergent faults. As we steepen dip angle, peak particle velocities in the homogeneous stress case generally increase in emergent faults but decrease in blind-thrust faults. Meanwhile, ground motion consistently increases with steepening dip angle under the stress gradient. We find that varying stress drop has a considerable scalar effect on both ground motion and permanent surface displacement, whereas changing fault strength has a negligible effect. Because of the simple geometry of a planar fault, our results can be applied to understanding basic behavior of specific real-world thrust faults.
Permanent sliding displacement analysis is commonly used to evaluate the seismic performance of slopes. Specifically, the fully probabilistic seismic slope displacement hazard analysis (PSSDHA) has attracted increasing attention recently, since it appropriately accounts for various sources of uncertainties associated with the estimation of sliding displacement. Within this analysis, the uncertainty of soil strength parameters (e.g., effective cohesion c' and effective internal friction angle ϕ′) is commonly quantified by a logic-tree method, in which the spatial variability of c' and ϕ′ is simply ignored. This study aims at proposing an extended PSSDHA framework by rigorously accounting for the spatial variability of c' and ϕ′, and then investigating its influence on the resultant slope displacement hazard curves based on the Newmark rigid-block model. Two different approaches, namely an analytical-based and a simulation-based method, are proposed separately. The results of the analytical-based method are found to be consistent with those obtained by the simulation-based one. It is also shown that the displacement hazard would be underestimated if the spatial variability of c' and ϕ′ is ignored; such underestimation is more significant for slopes with soil parameters exhibiting weak c'-ϕ ′ correlation and strong spatial variability. Besides, it suggests that the proper configuration of logic-tree framework plays an important role in developing displacement hazard curves, and a relatively large range of discrete strength values is recommended to better account for the effect of the spatial variability of soil parameters.
We use an epidemic-type aftershock sequence (ETAS) based approach to develop a regionally optimized background earthquake rates from ETAS (ROBERE) method for probabilistic seismic hazard assessment. ROBERE fits parameters to the full seismicity catalog for a region with maximum-likelihood estimation, including uncertainty. It then averages the earthquake rates over a suite of catalogs from which foreshocks and aftershocks have been removed using stochastic declustering while maintaining the same Gaussian smoothing currently used for the U.S. Geological Survey National Seismic Hazard Model (NSHM). The NSHM currently determines these rates by smoothing a single catalog from which foreshocks and aftershocks have been removed using the method of Gardner and Knopoff (1974; hereafter, GK74). The parameters used in GK74 were determined from subjectively identified aftershock sequences, unlike ROBERE, in which both background rate and aftershock triggering parameters are objectively fitted. A major difference between the impacts of the two methods is GK74 significantly reduces the b-value, a critical value for seismic hazard analysis, whereas ROBERE maintains the original b-value from the full catalog. We apply these methods to the induced seismicity in Oklahoma and Kansas and tectonic activity in the San Francisco Bay Region. Using GK74 gives lower overall earthquake rates but estimates higher hazard due to the reduction in the b-value. ROBERE provides higher earthquake rates, at the magnitude of completeness, but lower hazard because it does not alter the b-value. We test two other declustering methods that produce results closer to ROBERE but do not use objectively fit parameters, include uncertainty, and may not work as well in other areas. We suggest adopting ROBERE for the NSHM so that our hazard estimates are based on an objective analysis, including uncertainty, and do not depend strongly on potentially biased b-values, which was never the goal of the existing methodology.
In low-seismicity areas such as Europe, seismic records do not cover the whole range of variable configurations required for seismic hazard analysis. Usually, a set of empirical models established in such context (the Mediterranean Basin, northeast U.S.A., Japan, etc.) is considered through a logic-tree-based selection process. This approach is mainly based on the scientist’s expertise and ignores the uncertainty in model selection. One important and potential consequence of neglecting model uncertainty is that we assign more precision to our inference than what is warranted by the data, and this leads to overly confident decisions and precision. In this paper, we investigate the Bayesian model averaging (BMA) approach, using nine ground-motion prediction equations (GMPEs) issued from several databases. The BMA method has become an important tool to deal with model uncertainty, especially in empirical settings with large number of potential models and relatively limited number of observations. Two numerical techniques, based on the Markov chain Monte Carlo method and the maximum likelihood estimation approach, for implementing BMA are presented and applied together with around 1000 records issued from the RESORCE-2013 database. In the example considered, it is shown that BMA provides both a hierarchy of GMPEs and an improved out-of-sample predictive performance.
Empirical fragility curves derived from large post-disaster databases with data aggregated at municipality-level, commonly make the assumption that the ground motion intensity level is known and is determined at the centroid of each municipality from a ground motion prediction equation. A flexible Bayesian framework is applied here to the 1980 Irpinia database to explore whether more complex statistical models that account for sources of uncertainty in the intensity can significantly change the shape of the fragility curves. Through this framework the effect of explicitly modelling the uncertainty in the intensity, the spatial correlation of its intra-event component and the uncertainty due to the scatter of the buildings in the municipality are investigated. The analyses showed that the results did not change substantively with increased model complexity or the choice of prior. Nonetheless, informed decisions should be based on the defensible modelling of the significant variability in the data between municipalities.
We present the first probabilistic seismic hazard assessment (PSHA) specifically for the Shanxi rift system, north China, which has been defined as one of the areas of highest seismic hazard and risk in China in recent decades. We applied a Monte Carlo-based approach to PSHA, based on so far the most complete earthquake catalog available, a detailed zonation considering both seismicity distribution and local tectonic features, a logic tree of carefully selected ground-motion prediction equations, as well as a cautious consideration of actual local site effects for this region. Both areal sources (for Ms<6.0) and fault sources (for Ms≥6.0) were considered, and a synthetic earthquake catalog was generated through Monte Carlo simulation. A logic tree was applied to represent the epistemic uncertainty related to attenuation models for the rift system. Actual local site effects were incorporated and the stability of the results was also tested in this study. Our results show that nearly the entire rift system faces a significant seismic hazard and associated high seismic risk, as more than 80% of the population and the main economical infrastructure of Shanxi are concentrated here. The highest hazard is found in the areas around the north margin of Tianzhen fault and the north segment of Hengshan fault in the north, and in the Linfen basin and the area around Zhongtiaoshan fault in the south of the rift system. Our results are comparable to, but a refinement of, the results of previous probabilistic seismic hazard studies in the region. Deaggregation of seismic hazard for five large cities in the rift system indicates that the seismic hazard is most contributed by the nearby sources. Results obtained in this study provide a better understanding of the seismic hazard in the Shanxi rift system and can thereby help guiding earthquake risk mitigation in the future.
We study the inter- and intra-method variability of VS30 results by inverting/forward-modeling individual dispersion data for 31 seismographic stations located in California where combinations of surface-wave methods were applied and the minimum recorded wavelength from each method satisfies the 30-m depth criteria. These methods consist of noninvasive geophysical (active and passive surface-wave techniques) multi-station approaches, including the Multi-channel Analysis of Surface Waves (MASW; Rayleigh and Love waves), Spectral Analysis of Surface Waves (SASW), Microtremor Array [using Extended Spatial Autocorrelation (ESAC) processing methods], and Refraction Microtremor (ReMi) methods. Depending on the apparent geologic or seismic complexity of the site, field crews applied one or a combination of these methods whenever economically feasible to estimate the one-dimensional shear-wave velocity (VS) profile and calculate VS30, the time-averaged VS to a depth of 30 m. For each of the 31 sites, we find both types of variability in VS30 estimates generally remain insignificant (arithmetic mean of 5% difference). We also find similar results (3%) when we evaluate individual-method based VS30 estimates against composite-method based estimates. We note that VS30 values vary insignificantly when using a combination of complementary methods, e.g., active MASW data combined with passive MAM data, and that the most reliable results are also based on close fitting of the theoretical dispersion data to the representative (experimental) dispersion data.
History of earthquake’s damages have illustrated the high vulnerability and risks associated with failure of water transfer and distribution systems. Adequate mitigation plans to reduce such seismic risks are required for sustainable development. The first step in developing a mitigation plan is prioritizing the limited available budget to address the most critical mitigation measures. This paper presents an optimization model that can be utilized for financial resource allocation towards earthquake risk mitigation measures for water pipelines. It presents a framework that can be used by decision-makers (authorities, stockholders, owners and contractors) to structure budget allocation strategy for seismic risk mitigation measures such as repair, retrofit, and/or replacement of steel and concrete pipelines. A stochastic model is presented to establish optimal mitigation measures based on minimizing repair and retrofit costs, post-earthquake replacement costs, and especially earthquake-induced large losses. To consider the earthquake induced loss on pipelines, the indirect loss due to water shortage and business interruption in the industries which needs water is also considered. The model is applied to a pilot area to demonstrate the practical application aspects of the proposed model. Pipeline exposure database, built environment occupancy type, pipeline vulnerability functions, and regional seismic hazard characteristics are used to calculate a probabilistic seismic risk for the pilot area. The Global Earthquake Model’s (GEM) OpenQuake software is used to run various seismic risk analysis. Event-based seismic hazard and risk analyses are used to develop the hazard curves and maps in terms of peak ground velocity (PGV) for the study area. The results of this study show the variation of seismic losses and mitigation costs for pipelines located within the study area based on their location and the types of repair. Performing seismic risk analysis analyses using the proposed model provides a valuable tool for determining the risk associated with a network of pipelines in a region, and the costs of repair based on acceptable risk level. It can be used for decision making and to establish type and budgets for most critical repairs for a specific region.
This paper proposes a novel fully probabilistic framework for the performance‐based seismic design of structures and uses tuned inerter dampers (TID) installed in civil engineering structures subjected to seismic loads to illustrate its applicability. The framework proposed is based on stochastic reduced‐order models, which makes it computationally efficient and can be used for the design of TIDs installed in any complex nonlinear structures subjected to general nonstationary, non‐Gaussian stochastic processes. In this study, the TID is installed in a multi‐degree‐of‐freedom nonlinear structure that is subjected to synthetic seismic records. Numerical results show that the framework proposed is able to provide rigorous and robust values for the parameters of the TID. The design parameters obtained using the stochastic framework proposed are compared with benchmark deterministic approaches, tested also for a large data set of ground‐motion real records. It is shown that the stochastic approach provides insightful designs of the TID that are consistent with the site seismicity and the frequency content of the stochastic excitation.
We examine the source, path and site effects to strong ground motions during the 2018 northern Osaka earthquake (MJ 6.1, Mw 5.5-5.7) by spectral inversion and ground motion prediction equations (GMPEs) using strong motion records. It is found that the Q for paths is modeled using frequency f as 38f 1.34 by spectral inversion, which almost agrees with Q estimated by a previous study. The observed attenuation gradients for 5%-damped acceleration response spectra SA and peak ground velocity PGV are consistent to GMPEs for crustal earthquakes in western Japan. These results show that path effects are average as crustal earthquakes. The site amplification factors from the seismic bedrock for PGV and Fourier spectra at periods of 1 to 2 s are large in the northeast and southwest directions from the source. This result shows that one of the causes of large instrumental seismic intensity in these directions is site amplification factors. The SA at periods of 0.1 to 4 s after the correction by site amplification factors in the GMPEs are 1.3 to 1.6 times larger than the GMPEs for Mw 5.5 and 1.0 to 1.3 times larger than GMPEs for Mw 5.7. On the other hand, the SA at periods of 4 to 5 s is the average level. The flat level of acceleration source spectra called as short-period spectral level A is estimated to 5.1−5.2×10¹⁸ Nm at periods of 0.2 to 2 s by spectral inversion. The estimated A is larger than A for previous crustal earthquakes with the same seismic moment M0 and the empirical M0-A relations. From both the spectral inversion and the comparison with GMPEs revealed that the generation of strong ground motions from the source at periods of 0.1 to 4 s are larger than the average of crustal earthquakes with the same M0 in Japan. It was pointed out by previous studies that the northern Osaka earthquake was composed of a strike-slip fault and a dip-slip fault and that the rupture mainly propagated to the southwest direction on the strike-slip fault. Therefore, we examine the effects of near fault rupture directivity and the radiation pattern to strong ground motions by correcting the path and site effects using spectral inversion results. It is found that the spectra become larger at periods longer than about 0.5 s at stations in the southwest direction from the source. Especially the effects of transverse components are larger than radial components and transverse components have clear velocity pulses. On the other hand, the spectra at stations in the northeast direction become smaller. The effects of near fault rupture directivity and the radiation pattern for SA are almost reproduced by the previous empirical model on the average by using both the strike-slip and dip-slip faults. However, the effects at periods of 0.5 to 1 s are noticeably stronger than those predicted by the model and are interpreted to be the other cause of large instrumental seismic intensity from 6 lower to 5 lower in the southwest direction.
Amplification factors computed from the equivalent-linear method using the program RASCALS are used to develop constraints on the nonlinear soil response for possible use by the NGA ground-motion model developers. The site response computations covered site conditions with average V-S30 values ranging from 160 to 900 m/s, soil depths from 15 to 914 m, and peak accelerations of the input rock motion (V-S30=1100 m/s) between 0.01 g and 1.5 g. Four sets of nonlinear properties of the soils are used: EPRI, Peninsular Range, Imperial Valley, and Bay Mud. The first two soil models are used for V-S30 >= 270 m/s and the later two are used for V-S30 <= 190 m/s. Simple parametric models of the nonlinear amplification factors that are functions of the PGA on rock and V-S30 are developed for the EPRI and Peninsula models.
We develop empirical relationships to predict nonlinear (i.e., amplitude-dependant) amplification factors for 5% damped response spectral acceleration as a continuous function of average shear wave velocity in the upper 30 m, Vs-30. We evaluate amplification factors as residuals between spectral accelerations from recordings and modified rock attenuation relationships for active regions. Amplification at low- and mid-periods is shown to increase with decreasing Vs-30 and to exhibit nonlinearity that is dependent on Vs-30. The degree of nonlinearity is large for NEHRP Category E (Vs-30< 180 m/s) but decreases rapidly with Vs-30, and is small for Vs-30>similar to 300 m/s. The results can be used as Vs-30-based site factors with attenuation relationships. The results also provide an independent check of site factors published in the NEHRP Provisions, and apparent bias in some of the existing NEHRP factors is identified. Moreover, the results provide evidence that data dispersion is dependent on Vs-30.
We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01-10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5-8.5 (depending on fault mechanism) and distances ranging from 0-200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil.
The first phase of the Next Generation Attenuation (NGA) project has now finished, resulting in the publication of five new
sets of empirical ground-motion models for PGA, PGV and response spectral ordinates. These models mark a significant advancement
in the state-of-the-art in empirical ground-motion modelling and include many effects that are not accounted for in existing
European equations. Under the assumption that the Euro-Mediterranean database from which the European relationships are derived
is unlikely to drastically change in the near future, a prudent question to ask is: can the NGA models be applied in Europe?
In order to answer this question, the NGA model of Boore and Atkinson (PEER Report 2007/01, Pacific Earthquake Engineering
Research Center, Berkeley, CA, 234pp., 2007), which is shown to be representative of the NGA models as a suite, is compared
with the dataset used for the development of the most recent European empirical ground-motion models for response spectral
ordinates and peak ground velocity. The comparisons are made using analyses of model residuals and the likelihood approach
of Scherbaum et al. (Bull Seism Soc Am 94(6):2164–2185, 2004). The analyses indicate that for most engineering applications,
and particularly for displacement-based approaches to seismic design, the NGA models may confidently be applied within Europe.
Furthermore, it is recommended that they be used in conjunction with existing European models to provide constraint on finite-fault
effects and non-linear site response within logic-tree frameworks. The findings also point to the potential benefits of merging
the NGA and European datasets.
We present a model for estimating horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The model provides predictive relationships for the orientation-independent average horizontal component of ground motions. Relationships are provided for peak acceleration, peak velocity, and 5-percent damped pseudo-spectral acceleration for spectral periods of 0.01 to 10 seconds. The model represents an update of the relationships developed by Sadigh (1997) and incorporates improved magnitude and distance scaling forms as well as hanging-wall effects. Site effects are represented by smooth functions of average shear wave velocity of the upper 30 m (V-S30) and sediment depth. The new model predicts median ground motion that is similar to Sadigh (1997) at short spectral period, but lower ground motions at longer periods. The new model produces slightly lower ground motions in the distance range of 10 to 50 km and larger ground motions at larger distances. The aleatory variability in ground motion amplitude was found to depend upon earthquake magnitude and on the degree of nonlinear soil response, For large magnitude earthquakes, the aleatory variability is larger than found by Sadigh (1997).
Empirical ground-motion models for the rotation-independent average horizontal component from shallow crustal earthquakes are derived using the PEER NGA database. The model is applicable to magnitudes 5-8.5, distances 0-200 km, and spectral periods of 0-10 sec. In place of generic site categories (soil and rock), the site is parameterized by average shear-wave velocity in the top 30 m (V-S30) and the depth to engineering rock (depth to V-S=1000 m/s). In addition to magnitude and style-of-faulting, the source term is also dependent on the depth to top-of-rupture: for the same magnitude and rupture distance, buried ruptures lead to larger short-period ground motions than surface ruptures. The hanging-wall effect is included with an improved model that varies smoothly as a function of the source properties (M, dip, depth), and the site location. The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations. The short-period standard deviation model for soil sites is also distant-dependent due to nonlinear site response, with smaller standard deviations at short distances.
This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the "PEER NGA" (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane RJB, and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5-8 , RJB 200 km, and VS30= 180- 1300 m / s. DOI: 10.1193/1.2830434
An empirical model for estimating the horizontal pseudo absolute spectral accelerations (PSA) generated by shallow crustal earthquakes is presented in this paper. The model was selected to be simple and the model parameters were estimated using the recordings gathered as part of the New Generation Attenuation (NGA) project. These parameters are presented for sites with an average shear wave velocity in the upper 30 m, V S30 900 m / s, and for sites with 450 m / s V S30 900 m / s. Site-specific dynamic response calculations are recommended for estimating spectral ordinates for sites with V S30 180 m / s. Parameters for sites with 180 m / s V S30 450 m / s are not included in this paper. The median values of peak horizontal ground acceleration (PGA) and PSA for short periods are on the order of 15% to 20% lower for strike slip events and 30% to 40% lower for reverse events than those calculated using pre-NGA relationships. The differences decrease significantly at longer periods. The minimum values of the standard error terms (for moment magnitude, M 7.5) are about 15% to 30% larger and the maximum values of the standard error terms (for M 5) are about 2% to 12% larger than the pre-NGA values.
Site response simulations for the NGA project
- W J Silva
Silva, W. J., 2005. Site response simulations for the NGA project, Report prepared for the Pacific Earthquake Engineering Research Center.
Next generation attenuation (NGA) empirical ground motion models: can they be used in Europe?
- K W Campbell
- Y Bozorgnia
Campbell, K. W. and Y. Bozorgnia (2006). Next generation attenuation (NGA) empirical ground
motion models: can they be used in Europe?, First European Conference on Earthquake
Engineering and Seismology Geneva, Switzerland, 3-8 September 2006, Paper Number: 458
3D ground motion simulations in basins
- S M Day
- J Bielak
- D Dreger
- R Graves
- S Larsen
- K Olsen
- A Pitarka
Day, S. M., J. Bielak, D. Dreger, R. Graves, S. Larsen, K. Olsen, A. Pitarka (2005). 3D ground
motion simulations in basins, Final report prepared for the Pacific Earthquake Engineering
Research Center, Project 1A03.